a. Field of the Invention
The present invention relates to an ultra-high resolution reducing lens system and, more particularly, to an ultra-high resolution reducing lens system comprising two lens groups, i.e., a lens group I having negative refractive power and lens group II having positive refractive power, and used for photographing an image of an object on to a film for producing a microfilm.
B. Description of the Prior Art
For known reducing lens systems with magnification about .times.1/100, the aperture ratio is generally F1.4 to F1.6 and, therefore, the quantity of light decreases in the marginal portion of the field. Moreover, the working distance (here, the term "working distance" means the distance between the final lens surface of the lens system to the image surface) is short and it is inconvenient for actual use.
Some of known reducing lens systems have larger aperture ratios, i.e., about F1.0. For those lens systems, however, magnification is about .times.1/15 and this is unsatisfactory for making a microfilm.
When it is attempted to design a reducing lens system for which the aperture ratio is about F1.0 and still magnification is about .times.1/100, the number of lenses constituting the lens system becomes large and the lens system as a whole becomes necessarily large. Moreover, it is very difficult to make the working distance large. Especially, in such case, the quantity of light and resolution in the marginal portion decrease considerably. To prevent such decrease, it is essential to make symmetry of coma favourable. When, however, coma is corrected favourably, it becomes difficult to correct chromatic aberration favourably. So, it is very difficult to favourably correct both of coma and chromatic aberration at the same time.